Heat curable epoxy-acrylate compositions

ABSTRACT

This invention relates to a heat curable composition comprising 
     (a) a liquid, ethylenically unsaturated monomer, oligomer or prepolymer of the formula: ##STR1##  wherein R is H or CH 3 , R 1  is an organic moiety and n is at least 2, 
     (b) an epoxy resin containing at least two ##STR2##  groups, and (c) a thermal initiator member of the group consisting of 
     (1) a substituted or unsubstituted diaryliodonium salt in combination with a free radical initiator, 
     (2) a BF 3  adduct, 
     (3) a BF 3  adduct in combination with a free radical initiator, and 
     (4) dicyandiamide in combination with a free radical initiator. 
     The system is stable at ordinary temperatures, but on heating the thermal initiator catalyzes the curing of the acrylate and the epoxy resin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a heat curable acrylate-epoxy resincomposition. The initiator system for the composition is stable atordinary temperatures but on heating the thermal initiator catalyzes thecocuring of the acrylate and the epoxy resin. The composition can beused to form adhesives, coatings and sealants.

2. Description of the Prior Art

It is known from U.S. Pat. No. 4,225,691 that the diaryliodonium saltsare operable per se to initiate curing of epoxy resins. The curing ratehowever is of the order of 30 minutes or more.

It is also known from U.S. Pat. No. 4,288,527 to expose a compositioncomprising an ethylenically unsaturated compound, photoinitiator and asubstituted or unsubstituted pinacol to UV radiation and heat inseriatium or simultaneously to obtain a cured solid product.

It is well known that BF₃ adducts and dicyandiamide will each cure epoxyresins per se.

OBJECTS OF THE INVENTION

One object of the instant invention is to produce an adhesivecomposition which is solventless. Another object of the invention is toproduce a composition which can be used as a sealant or coating. Stillanother object of the instant invention is to produce an adhesivecomposition which is heat curable in a minimum time period. Otherobjects will become apparent from a reading hereinafter.

DESCRIPTION OF THE INVENTION

This invention relates to a heat curable composition comprising

(a) a liquid, ethylenically unsaturated monomer, oligomer or prepolymerof the formula: ##STR3## wherein R is H or CH₃, R₁ is an organic moietyand n is at least 2,

(b) an epoxy resin containing at least two ##STR4## groups, and

(c) a thermal initiator member of the group consisting of

(1) a substituted or unsubstituted diaryliodonium salt in combinationwith a free radical initiator,

(2)a BF₃ adduct,

(3) a BF₃ adduct in combination with a free radical initiator, and

(4) dicyandiamide in combination with a free radical initiator.

The system is stable at ordinary temperatures, but on heating thethermal initiator catalyzes the curing of the acrylate and the epoxyresin.

The composition after application to the parts to be bonded or sealedforms a thermoset bond or seal on application of heat thereto,preferably by high frequency techniques including dielectric orinduction heating. Although the composition and process taught herein isoperable to form a thermoset coating bond or seal, the invention for themost part for reasons of brevity will be explained in terms of adhesivebonding.

The liquid ethylenically unsaturated monomer, oligomer or prepolymer,i.e., the acrylate terminated polyene, of the formula: ##STR5## whereinR is H or CH₃, R₁ is an organic moiety and n is at least 2 of thecomposition herein, can be made by various reactants and methods. One ofthese acrylate terminated materials is a polyether polyol urethanepolyacrylate formed by reacting a polyether polyol with a polyisocyanateand a hydroxyalkyl acrylate. Another material may be a polyester polyolurethane polyacrylate formed by reacting a polyester polyol with apolyisocyanate and a hydroxyalkyl acrylate. Still another material inthis category is an epoxy acrylate formed by reacting a diepoxide withacrylic acid. Yet another acrylate terminated material operable hereinis a polyether or a polyester acrylate formed by end-capping a polyetherpolyol or polyester polyol with acrylic acid or acryoyl chloride. Yetanother acrylate terminated material operable herein is a urethanepolyacrylate formed by end-capping a diisocyanate with a hydroxyalkylacrylate. As used herein, the term "acrylate" refers to both acrylatesand methacrylates. Examples of the above acrylate terminated materialsinclude, but are not limited to, 1,3-butylene glycol diacrylate,diethylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentylglycol diacrylate, polyethylene glycol 200 diacrylate, tetraethyleneglycol diacrylate, triethylene glycol diacrylate, pentaerythritoltetraacrylate, tripropylene glycol diacrylate, ethoxylated bisphenol-Adiacrylate, trimethylolpropane triacrylate, di-trimethylol propanetetraacrylate, triacrylate of tris(hydroxyethyl)isocyanate,dipentaerythritol pentaacrylate, pentaerythritol triacrylate,ethoxylated trimethylolpropane tiracrylate, triethylene glycoldimethacrylate, ethylene glycol dimethacrylate, tetraethylene glycoldimethacrylate, polyethylene glycol-200 dimethacrylate, 1,6-hexanedioldimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycol-600dimethacrylate, 1,3-butylene glycol dimethacrylate, ethoxylatedbisphenol-A dimethacrylate, trimethylolpropane trimethacrylate,diethylene glycol dimethacrylate, 1,4-butanediol diacrylate, diethyleneglycol dimethacrylate, pentaerythritol tetramethacrylate, glycerindimethacrylate, trimethylolpropane dimethacrylate, pentaerythritoltrimethacrylate, pentaerythritol dimethacrylate and pentaerythritoldiacrylate.

The epoxy resin to be used in the composition of the invention comprisesthose materials possessing at least two epoxy, i.e., ##STR6## groups.These compounds may be saturated or unsaturated, aliphatic,cycloaliphatic, aromatic or heterocyclic and may be substituted withsubstituents, such as chlorine, hydroxyl groups, ether radicals and thelike.

The term "epoxy resin" when used herein and in the appended claimscontemplates any of the conventional monomeric, dimeric, oligomeric orpolymeric epoxy materials containing a plurality, at least 2, epoxyfunctional groups. Preferably, they will be members of classes describedchemically as (a) an epoxidic ester having two epoxycycloalkyl groups;(b) an epoxy resin prepolymer consisting predominately of the monomericdiglycidyl ether of bisphenol-A; (c) a polyepoxidized phenol novolak orcresol novolak; (d) a polyglycidyl ether of a polyhydric alcohol; (e)diepoxide of a cycloalkyl or alkylcycloalkyl hydrocarbon or ether; or(f) a mixture of any of the foregoing. To save unnecessarily detaileddescription, reference is made to the Encyclopedia of Polymer Scienceand Technology, Vol. 6, 1967, Interscience Publishers, New York, pages209-271.

Suitably commercially available epoxidic esters are preferably,3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (Union CarbideERL 4221, Ciba Geigy CY-179); as well asbis(3,4-epoxy-6-methylcyclohexylmethyl)adipate (Union Carbide ERL 4289);and bis(3,4-epoxycyclohexylmethyl)adipate (Union Carbide ERL 4299).

Suitable commercially available diglycidyl ethers of bisphenol-A areCiba Geigy Araldite 6010, Dow Chemical DER 331, and Shell Chemical Epon828 and 826.

A polyepoxidized phenol formaldehyde novolak prepolymer is availablefrom Dow Chemixcal DEN 431 and 438 and a polyepoxidized cresolformaldehyde novolak prepolymer is available from Ciba-Geigy Araldite538.

A polyglycidyl ether of a polyhydric alcohol is available from CibaGeigy, based on butane-1,4-diol, Araldite RD-2; and from Shell ChemicalCorp., based on glycerine, EPON 812.

A suitable diepoxide of an alylycycloalkyl hydrocarbon is vinylcyclohexene dioxide, Union Carbide ERL 4206; and a suitable diepoxide ofa cycloalkyl ether is bis(2,3-epoxycyclopentyl)-ether, Union Carbide ERL0400.

Other examples include the epoxidized esters of the polyethylenicallyunsaturated monocarboxylic acids, such as epoxidized linseed, soybean,perilla, oiticica, tung, walnut and dehydrated castor oil, methyllinoleate, butyl lineoleate, ethyl 9,12-octadecadienoate, butyl9,12,15-octadecatrienoate, butyl eleostearate, monoglycerides of tungoil fatty acids, monoglycerides of soybean oil, sunflower, rapeseed,hempseed, sardine, cottonseed oil and the like.

The free radical initiators used herein are selected from substituted orunsubstituted pinacols, azo compounds, thiurams, organic peroxides andmixtures thereof.

The organic peroxides operable are of the general formula:

    R--O--O--(R.sub.1 --O--O).sub.n --R

wherein n=0 or 1, R is independently selected from hydrogen, aryl,alkyl, aryl carbonyl, alkaryl carbonyl, aralkyl carbonyl and alkylcarbonyl and R₁ is alkyl or aryl, said alkyl groups containing 1 to 20carbon atoms.

Examples of operable organic peroxides include, but are not limited to2,5-dimethyl-2,5-di(t-butylperoxy)-hexane,1,3-bis(t-butylperoxyisopropyl)benzene,1,3-bis-(cumylperoxyisopropyl)benzene, 2,4-dichlorobenzoyl peroxide,caprylyl peroxide, lauroyl peroxide, t-butyl peroxyisobutyrate, benzoylperoxide, p-chlorobenzoyl peroxide, hydroxyheptyl peroxide, di-t-butyldiperphthalate, t-butyl peracetate, t-butyl perbenzoate, dicumylperoxide, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane anddi-t-butyl peroxide.

The organic peroxide is added to the composition in an amount rangingfrom 0.01-10%, preferably 0.1-5%, by weight based on the weight of theethylenically unsaturated group member.

Examples of azo compounds operable herein include, but are not limitedto, commercially available compounds such as2-t-butylazo-2-cyanopropane;2,2'-azobis(2,4-dimethyl-4-methoxy-valeronitrile);2,2'-azobis(isobutyronitrile); 2,2'-azobis(2,4-dimethylvaleronitrile)and 1,1'-azobis(cyclohexanecarbonitrile).

The azo compound is added to the composition in an amount ranging from0.001-5%, preferably 0.01-2% by weight based on the weight of theethylenically unsaturated group member.

The thiurams operable as thermal initiators herein are of the formula##STR7## wherein R₁, R₂, R₃ and R₄ taken singly can be hydrogen, linearor branched alkyl having from 1 to about 12 carbon atoms, linear orbranched alkenyl having from 2 to about 12 carbon atoms, cycloalkylhaving from 3 to about 10 ring carbon atoms, cycloalkenyl having from 3to about 10 ring carbon atoms, aryl having from 6 to about 12 ringcarbon atoms, alkaryl having from 6 to about 12 ring carbon atoms,aralkyl having from 6 to about 12 ring carbon atoms and, when takentogether, R₁ and R₂ and R₃ and R₄ can each be a divalent alkylene group(--C_(n) H_(2n) --) having from 2 to about 12 carbon atoms, a divalentalkenylene group (C_(n) H_(2n-2)) group having from 3 to about 10 carbonatoms, a divalent alkadienylene group --(C_(n) H_(2n-) 4)--having from 5to about 10 carbon atoms, a divalent alkatrienylene group (C_(n)H_(2n-6)) having from 5 to about 10 carbon atoms, a divalentalkyleneoxyalkylene group (--C_(x) H_(2x) OC_(x) H_(2x) --) having atotal of from 4 to about 12 carbon atoms or a a divalentalkyleneaminoalkylene group ##STR8## having a total of from 4 to about12 carbon atoms.

Operable thiurams include, but are not limited to, tetramethylthiuramdisulfide, tetraethylthiuram disulfide, di-N-pentamethylenethiuramdisulfide, tetrabutylthiuram disulfide, diphenyldimethylthiuramdisulfide, diphenyldiethylthiuram disulfide and diethyleneoxythiuramdisulfide and the like.

The thiuram is added to the composition in an amount ranging from0.005-5.0% by weight of the ethylenically unsaturated group member.

The substituted or unsubstituted pinacols operable herein as a thermalinitiator in combination with either the diaryliodonium salt, BF₃ adductor dicyandiamide have the general formula: ##STR9## wherein R₁ and R₃are the same or different substituted or unsubstituted aromaticradicals, R₂ and R₄ are substituted or unsubstituted aliphatic oraromatic radicals and X and Y which may be the same or different arehydroxyl, alkoxy or aryloxy.

Preferred pinacols are those wherein R₁, R₂, R₃ and R₄ are aromaticradicals, especially phenyl radical and X and Y are hydroxyl.

Examples of this class of compounds include, but are not limited to,benzopinacol, 4,4'-dichlorobenzopinacol, 4,4'-dibromobenzopinacol,4,4'-diiodobenzopinacol, 4,4',4",4"'-tetrachlorobenzopinacol,2,4,2',4'-tetrachlorobenzopinacol, 4,4'-dimethylbenzopinacol,3,3'-dimethylbenzopinacol, 2,2'-dimethylbenzopinacol,3,4,3',4'-tetramethylbenzopinacol, 4,4'-dimethoxybenzopinacol, 4,4',4",4"'-tetramethoxybenzopinacol, 4,4'-diphenylbenzopinacol,4,4'-dichloro-4",4"'-dimethylbenzopinacol,4,4'-dimethyl-4",4"'-diphenylbenzopinacol, xanthonpinacol,fluoroenonepinacol, acetophenonepinacol,4,4'-dimethylacetophenone-pinacol, 4,4'-dichloroacetophenonepinacol,1,1,2-triphenyl-propane-1,2-diol, 1,2,3,4-tetraphenylbutane-2,3-diol,1,2-diphenylcyclobutane-1,2-diol, propiophenone-pinacol,4,4'-dimethylpropiophenone-pinacol,2,2'-ethyl-3,3'-dimethoxypropiophenone-pinacol,1,1,1,4,4,4-hexafluoro-2,3-diphenyl-butane-2,3-diol.

As further compounds according to the present invention, there may bementioned: benzopinacol-mono methylether, benzopinacol-mono-phenylether,benzopinacol and monoisopropyl ether, benzopinacol monoisobutyl ether,benzopinacol mono (diethoxy methyl) ether and the like.

The pinacol is added to the composition in amounts ranging from0.01-10%, preferably 0.1-5%, by weight based on the weight of theethylenically unsaturated group member.

The BF₃ adducts used herein as thermal initiators include, but are notlimited to, C₆ H₅ NH₂.BF₃, 2,6-Et₂ C₆ H₃ NH₂.BF₃, EtNH₂.BF₃, sec-Bu₂NH.BF₃, Et₂ NH.BF₃, (C₆ H₅)₃ P.BF₃, C₆ H₅ NMe₂.BF₃, Pyridine . BF₃, andEt₃ N.BF₃, Et₂ O.BF₃, (HOCH₂ CH₂)₃ N.BF₃.

The diaryliodonium salts operable herein as thermal initiators incombination with a pinacol are those set out in U.S. Pat. No. 4,238,587,and it is understood that so much of the disclosure therein relative tothe diaryliodonium salts is incorporated herein by reference. That is,the diaryliodonium salts which can be utilized in the practice of theinvention are shown as follows:

    [(R).sub.a (R.sup.1).sub.b I].sup.+ [Y].sup.-,             (1)

where R is a C.sub.(6-13) aromatic hydrocarbon radical, R¹ is a divalentaromatic organic radical, and Y is an anion, a is equal to 0 or 2, b isequal to 0 or 1 and the sum of a+b is equal to 1 or 2. Preferably, Y isan MQ_(d) anion where M is a metal or metalloid, Q is a halogen radicaland d is an integer equal to 4-6.

Radicals included within R of formula (1) can be the same or differentaromatic carbocyclic radicals having from 6 to 20 carbon atoms, whichcan be substituted with from 1 to 4 monovalent radicals selected fromC.sub.(1-8) alkoxy, C.sub.(1-8) alkyl, nitro, chloro, etc. R is moreparticularly phenyl, chlorophenyl, nitrophenyl, methoxyphenyl, pyridyl,etc. Radicals included by R¹ of formula (1) are divalent radicals suchas ##STR10## where Z is selected from --O--, --S--, ##STR11## R² isC.sub.(1-8) alkyl or C.sub.(6-13) aryl, and n is an integer equal to 1-8inclusive.

Metals or metalloids included by m of formula (1) are transition metalssuch as Sb, Fe, Sn, Bi, Al, Ga, In, Ti, Zr, Sc, V, Cr, Mn, Cs, rareearth elements such as the lanthanides, for example, Cd, Pr, Nd, etc.,actinides, such as Th, Pa, U, Np, etc., and metalloids such as B, P, As,Sb, etc. Complex anions included by MQ_(d) are, for example, BF₄ ⁻, PF₆⁻, AsF₆ ^(`), SbF₆ ⁻, FeCl₄ ₋, SnCl₆ ⁻, SbCl₆ ⁻, BiCl₅ ⁻⁻, etc.

Some of the diaryliodonium salts which can be used in the practice ofthe invention are as follows: ##STR12##

These thermal initiators are added to the system in an amount rangingfrom 1 to 10% by weight of the epoxy resin.

Thus, when an ethylenically unsaturated group member and an epoxy resinare added in combination to form a thermoset adhesive, in some instancesit is necessary to add as a thermal initiator both the aforementionedfree radical type and the ionic type in the amounts specified in orderto obtain a cocured adhesive. The BF₃ adduct is operable per se toinitiate the crosslinking reaction but preferably is used in combinationwith a free radical initiator disclosed herein due to the faster curerate.

The thermal initiator can be added to the system in various ways. Thatis, the thermal initiator, per se, can be admixed with the ethylenicallyunsaturated or epoxy group member. Additionally, the thermal initiatorcan be dissolved or suspended in a minor amount of well knowncommercially available solvents such as dibutyl phthalate; ketones,e.g., acetone and methylethyl ketone or chlorinated hydrocarbons such asmethylene chloride, and then added to the system.

In practicing the instant invention, the components of the heatactivatable adhesive composition can be present in widely varyingamounts depending on the end use of the composition. That is, theethylenically unsaturated or epoxy group member can be present in anamount ranging from 5 to 95% by weight. The percentages of thermalinitiators used have previously been set out herein and are based on theweight percent of the ethylenically unsaturated or epoxy group memberpresent.

The compositions of the present invention may, if desired, include suchadditives as antioxidants, inhibitors, fillers, antistatic agents,flame-retardant agents, thickeners, thixotropic agents, surface-activeagents, viscosity modifiers, plasticizers, tackifiers and the likewithin the scope of this invention. Such additives are usuallypreblended with the ethylenically unsaturated or epoxy compound prior toor during the compounding step. Operable fillers which can be added tothe system to reduce cost include natural and synthetic resins, glassfibers, wood flour, clay, silica, alumina, carbonates, oxides,hydroxides, silicates, glass flakes, borates, phosphates, diatomaceousearth, talc, kaolin, barium sulfate, calcium sulfate, calcium carbonate,wollastonite, carbon fibers and the like. The aforesaid additives may bepresent in quantities up to 500 parts or more per 100 parts of thecomposition by weight and preferably about 0.005 to about 300 parts onthe same basis.

Additionally, scavengers and antioxidants such as hydroquinone,pyrogallol, phosphorous acid, tert-butyl hydroquinone, tert-butylcatechol, p-benzoquinone, 2,5-diphenylbenzo-quinone,2,6-di-tert-butyl-p-cresol, etc., are added to the system inconventional amounts ranging from 0.001 to 2.0% by weight of theethylenically unsaturated member.

Additionally, epoxy resin stabilizers such as phosphites, e.g.,triphenyl phosphite, diphenyl phosphite and trisnonylphenyl phosphiteare added to the system in conventional amounts ranging from 0.001 to2.0% by weight of the epoxy esin.

The heating step is usually carried out for a period of 10 seconds to 30minutes at a temperature of 80°-300° C., preferably 100°-200° C. whichis sufficient to fully cure the composition to a solid adhesive, coatingor sealant product.

The heating step using a thermal initiator to cure the adhesive organicresin composition can be accomplished in several ways. In simplesystems, the adhesive composition can be applied by manual means to anadherend, contacted with another adherend and the assembled systemheated in a forced air oven until a thermoset bond results.

Additionally and preferably, electromagnetic heating can be utilized asa faster and more efficient means of curing, especially where thesubstrates to be bonded are plastic materials. In addition to theformation of high strength bonds, electromagnetic bonding techniques aidin (a) fast bond setting times, and (b) automated part handling andassembly.

In practicing the instant invention, electromagnetic heating can beemployed with the adhesive composition herein to adhere (1) plastic toplastic, (2) plastic to metal and (3) metal to metal. For example,dielectric heating can be used to bond (1) and (2) supra if the adhesivecomposition contains sufficient polar groups to heat the compositionrapidly and allow it to bond the adherends. Inductive heating can alsobe used to bond (1), (2) and (3). That is, when at least one of theadherends is an electrically conductive or ferromagnetic metal, the heatgenerated therein is conveyed by conductance to the adhesive compositionthereby initiating the cure to form a thermoset adhesive. In theinstance where both adherends are plastic, it is necessary to add anenergy absorbing material, i.e., an electrically conductive orferromagnetic material, preferably in fiber or particle form (10-400mesh) to the adhesive composition. The energy absorbing material isusually added in amounts ranging from 0.1 to 2 parts by weight, per 1part by weight of the adhesive organic resin composition. It is alsopossible to impregnate the plastic adherend at the bonding joint withparticles of the energy absorbing material in order to use inductiveheating, but care must be exercised that the plastic is not distorted.

The particulate electromagnetic energy absorbing material used in theadhesive composition when induction heating is employed can be one ofthe magnetizable metals including iron, cobalt and nickel ormagnetizable alloys or oxides of nickel and iron and nickel and chromiumand iron oxide. These metals and alloys have high Curie points(730°-2,040° F.).

Electrically conductive materials operable herein when inductive heatingis employed include, but are not limited to, the noble metals, copper,aluminum, nickel, zinc as well as carbon black, graphite and inorganicoxides.

There are two forms of high frequency heating operable herein, thechoice of which is determined by the material to be adhered. The majordistinction is whether or not the material is a conductor ornon-conductor of electrical current. If the material is a conductor,such as iron or steel, then the inductive method is used. If thematerial is an insulator, such as wood, paper, textiles, syntheticresins, rubber, etc., then dielectric heating can also be employed.

Most naturally occurring and synthetic polymers are non-conductors and,therefore, are suitable for dielectric heating. These polymers maycontain a variety of dipoles and ions which orient in an electric fieldand rotate to maintain their aignment with the field when the fieldoscillates. The polar groups may be incorporated into the polymerbackbone or can be pendant side groups, additives, extenders, pigments,etc. For example, as additives, lossy fillers sch as carbon black at aone percent level can be used to increase the dielectric response of theadhesive. When the polarity of the electric field is reversed millionsof times per second, the resulting high frequency of the polar unitsgenerates heat within the material.

The uniqueness of dielectric heating is in its uniformity, rapidity,specificity and efficiency. Most plastic heating processes such asconductive, convective or infrared heating are surface-heating processeswhich need to establish a temperature within the plastic andsubsequently transfer the heat to the bulk of the plastic by conduction.Hence, heating of plastics by these methods is a relatively slow processwith a non-uniform temperature resulting in overheating of the surfaces.By contrast, dielectric heating generates the heat within the materialand is therefore uniform and rapid, eliminating the need for conductiveheat transfer. In the dielectric heating system herein the electricalfrequency of the electromagnetic field is in the range 1-3,000megahertz, said field being generated from a power source of 0.5-1,000kilowatts.

Induction heating is similar, but not identical, to dielectric heating.The following differences exist: (a) magnetic properties are substitutedfor dielectric properties; (b) a coil is employed to couple the loadrather than electrodes or plates; and (c) induction heaters couplemaximum current to the load. The generation of heat by inductionoperates through the rising and falling of a magnetic field around aconductor with each reversal of an alternating current source. Thepractical deployment of such field is generally accomplished by properplacement of a conductive coil. When another electrically conductivematerial is exposed to the field, induced current can be created. Theseinduced currents can be in the form of random or "eddy" currents whichresult in the generation of heat. Materials which are both magnetizableand conductive generate heat more readily than materials which are onlyconductive. The heat generated as a result of the magnetic component isthe result of hysteresis or work done in rotating magnetizable moleculesand as a result of eddy current flow. Polyolefins and other plastics areneither magnetic nor conductive in their natural states. Therefore, theydo not, in themselves, create heat as a result of induction.

The use of the eletromagnetic induction heating method for adhesivebonding of plastic structures has proved feasible by interposingselected eletromagnetic energy absorbing materials in an independentadhesive composition layer or gasket conforming to the surfaces to bebonded, electromagnetic energy passing through the adjacent plasticstructures (free of such energy absorbing materials) is readilyconcentrated and absorbed in the adhesive composition by such energyabsorbing materials thereby rapidly initiating cure of the adhesivecomposition to a thermoset adhesive.

Electromagnetic energy absorbing materials of various types have beenused in the electromagnetic induction heating technique for some time.For instance, inorganic oxides and powdered metals have beenincorporated in bond layers and subjected to electromagnetic radiation.In each instance, the type of energy source influences the selection ofenergy absorbing material. Where the energy absorbing material iscomprised of finely divided particles having ferromagnetic propertiesand such particles are effectively insulated from each other by particlecontaining nonconducting matrix material, the heating effect issubstantially confined to that resulting from the effects of hysteresis.Consequently, heating is limited to the "Curie" temperature of theferromagnetic material or the temperature at which the magneticproperties of such material cease to exist.

The electromagnetic adhesive composition of this invention may take theform of an extruded ribbon or tape, a molded gasket or cast sheet. Inliquid form it may be applied by brush to surfaces to be bonded or maybe sprayed on or used as a dip coating for such surfaces.

The foregoing adhesive composition, when properly utilized as describedhereinafter, results in a solvent free bonding system which permits thejoining of metal or plastic items without costly surface pretreatment.The electromagnetically induced bonding reaction occurs rapidly and isadaptable to automated fabrication techniques and equipment.

To accomplish the establishment of a concentrated and specificallylocated heat zone by induction heating in the context of bonding inaccordance with the invention, it has been found that theelectromagnetic adhesive compositions described above can be activatedand a bond created by an induction heating system operating with anelectrical frequency of the electromagnetic field of from about 5 toabout 30 megacycles and preferably from about 15 to 30 megacycles, saidfield being generated from a power source of from about 1 to about 30kilowatts, and preferably from about 2 to about 5 kilowatts. Theelectromagnetic field is applied to the articles to be bonded for aperiod of time of less than about 2 minutes.

As heretofore mentioned, the electromagnetic induction bonding systemand improved electromagnetic adhesive compositions of the presentinvention are applicable to the bonding of metals, thermoplastic andthermoset material, including fiber reinforced thermoset material.

The following examples are set out to explain, but expressly not limit,the instant invention. Unless otherwise noted, all parts and percentagesare by weight.

Strength properties of adhesive in shear by tension loading were run inaccord with ASTMD 1002-64 based on one inch square of lapped area unlessotherwise specified.

EXAMPLE 1 Preparation of Iodobenzene Diacetate

40.8 g (0.2 mol) of iodobenzene were charged to a 300 ml round bottomflask equipped with thermometer and vented addition funnel. 91.2 g (0.48mol) of a 40% aqueous solution of peracetic acid was added dropwise tothe flask over a 25-minute period while maintaining the flask at 30° C.in a water bath. After about 1 hour a yellowish white solid formed. Thereaction mixture was cooled in ice and the solid collected, washed withwater and vaccuum dried at 40° C. The iodobenzene diacetate productweighed 40.6 g and had a melting point in the range of 157°-160° C.

EXAMPLE 2 Preparation of 4-Methoxydiphenyliodonium Tetrafluoroborate

48.6 g iodobenzene diacetate, 16.3 ml anisole, 65 ml acetic anhydrideand 725 ml glacial acetic acid were charged to a 2 liter, 3 neck roundbottom flask equipped with stirrer, reflex condenser, thermometer andaddition funnel. 8 ml of concentrated sulfuric acid were added dropwiseover a 20 minute period to the flask while maintaining the temperaturebelow 10° C. A viscous brown mixture containing white needles formed.The mixture was thawed to room temperature over a 11/2 hour period atwhich point it was stirred for an additional 45 minutes at roomtemperature. 31 g of sodium bromide in 150 cc of water were added to thesolution. Ten solid particles formed which were collected, washed withwater and dried. The resultant product, i.e., 47 g of4-methoxydiphenyliodonium bromide, had a melting point of 165°-168° C.

39.9 g of the 4-methoxydiphenyliodonium bromide were dissolved in 1,000cc of water and 500 cc of acetone with heating. To this solution wereadded 25 g (0.13 moles) of silver tetrafluoroborate in 40 cc of water.The silver bromide formed was removed by filtration and the filtrate wasreduced in volume by 2/3 in a Buchi rotovapor resulting in a brownliquid which was then refrigerated. 26.8 g of white and brown dampsolids were collected from the refrigerated material and dissolved in100 cc CH₂ Cl₂ and passed through a 1" by 3" long neutral aluminacolumn. 100 cc of pale brown liquid was collected. 150 cc of ether weremixed in with the pale brown liquid resulting in the formation of whitesolids. The white solids were collected, washed with ether and dried.The resultant white solid product weighed 13.3 g and had a melting pointof 104°-105° C. Another 50 cc of the CH₂ Cl₂ from the alumina columnwere collected, washed with ether and dried. The dried product weighed2.5 g and had a melting point of 98°-99° C. The two resultant productswere admixed together. The NMR spectrum of the product was in agreementwith the structure for 4-methoxydiphenyliodonium tretrafluoroborate.

Analysis. Calcd. for C₁₃ H₁₂ BF₄ IO: C, 39.22; H, 3.02; B, 2.72; F,19.11; I, 31.91. Found: C, 39.85; H, 3.02; B, 2.75; F, 17.54; I, 32.78.

EXAMPLE 3 Preparation of Diphenyliodonium Tetrafluoroborate

20 g of silver tetrafluoroborate were dissolved in 20 g of water in abeaker at 60° C. with stirring. 33.52 g of 97% diphenyliodonium chloridewere dissolved in 720 g of water in another beaker at 60° C. withstirring. The silver tetrafluoroborate solution was slowly poured intothe diphenyliodonium chloride solution and the AgCl precipitate wasremoved by filtration. The filtrate was refrigerated for 2 daysresulting in the formation of white crystals. The filtrate was thawedand refiltered. The resulting white crystal solids from this filtrationwere washed with water, air dried and then vacuum dried over night toobtain 11.1 g of white crystals. The filtrate was reduced to 2/3 itsvolume in a Bucchi rotovapor and then refrigerated. After thawing atroom temperature the filtrate was refiltered and the white crystals werecollected as set out above. The two resultant long white needle productsweighed 28.6 g and had a melting point in the range 132°-137° C.

Analysis. Calcd. for C₁₂ H₁₀ BF₄ I: C, 39.16; H, 2.72; B, 2.94; F,20.67; I, 34.51. Found: C, 39.15; H, 2.64; B, 3.04; F, 20.55; I, 34.98.

The following examples show heat curing of the composition:

EXAMPLE 4

The following mixtures were made up by stirring the components togetherat room temperature:

    ______________________________________                                        (a)   trimethylolpropane triacrylate                                                                       2.5 g                                                  1,4-butanediol diepoxide                                                                             7.5 g                                                  benzopinacol           0.3 g                                                  4-methoxydiphenyliodonium tetrafluoro-                                        borate                 0.3 g                                            (b)   1,4-butanediol diepoxide                                                                             5.0 g                                                  trimethylolpropane triacrylate                                                                       5.0 g                                                  Leepoxy B-550 (BF.sub.3 adduct,                                               commercially available from Leepoxy)                                                                 0.3 g                                                  benzopinacol           0.3 g                                            (c)   1,4-butanediol diepoxide                                                                             5.0 g                                                  trimethylolpropane triacrylate                                                                       5.0 g                                                  Leepoxy B-550          0.3 g                                            (d)   1,4-butanediol diepoxide                                                                             5.0 g                                                  trimethylolpropane triacrylate                                                                       5.0 g                                                  Leepoxy B-550          0.3 g                                                  1,1-di(ti-butylperoxy)-3,3,5-trimethyl-                                       cyclohexane            0.1 g                                            ______________________________________                                    

Each mixture in a 30 ml beaker was placed in a 120° C. air oven until itbecame solid and the time required to solidify was recorded for eachmixture as shown in TABLE I:

                  TABLE I                                                         ______________________________________                                        Mixture     Time to Solidify (sec)                                            ______________________________________                                        (a)         250                                                               (b)         320                                                               (c)         730                                                               (d)         440                                                               ______________________________________                                    

EXAMPLE 5

The following mixtures were made up by stirring the components togetherat room temperature:

    ______________________________________                                        (e)   trimethylolpropane triacrylate                                                                        5.0 g                                                 1,4-butanediol diepoxide                                                                              5.0 g                                                 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclo-                                   hexane                  0.3 g                                                 diphenyliodonium tetrafluoroborate                                                                    0.3 g                                           (f)   1,4-butanediol diepoxide                                                                              5.0 g                                                 trimethylolpropane triacrylate                                                                        5.0 g                                                 diphenyliodonium tetrafluoroborate                                                                    0.3 g                                                 tetramethylthiuram disulfide                                                                          0.1 g                                           (g)   1,4-butanediol diepoxide                                                                              5.0 g                                                 trimethylolpropane triacrylate                                                                        5.0 g                                                 diphenyliodonium tetrafluoroborate                                                                    0.3 g                                                 2,2-azobis(isobutyronitrile)                                                                          0.3 g                                           (h)   1,4-butanediol diepoxide                                                                              2.5 g                                                 trimethylolpropane triacrylate                                                                        7.5 g                                                 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclo-                                   hexane                  0.3 g                                                 dicyandiamide           0.6 g                                           ______________________________________                                    

Each mixture was put in a 4 dram vial and placed in a 170° C. air ovenuntil it became solid. The time required to solidify was recorded foreach mixture as shown in TABLE II:

                  TABLE II                                                        ______________________________________                                        Mixture     Time to Solidify (sec)                                            ______________________________________                                        (e)         164                                                               (f)         488                                                               (g)         110                                                               (h)         234                                                               ______________________________________                                    

EXAMPLE 6

2.5 g of 1,4-butanediol diepoxide, 7.5 g of trimethylolpropanetriacrylate, 0.3 g of 4-methoxydiphenyliodonium tetrafluoroborate fromExample 2 and 0.3 g of benzopinacol were mixed together by stirring atroom temperature in a 30 ml beaker. The beaker was then placed in an airoven heated to 160° C. The mixture cured to a black solid in 3 minutes.

EXAMPLE 7

10 g of 1,4-butanediol diepoxide, 10 g of trimethylolpropanetriacrylate, 0.6 g of diphenyliodonium tetrafluoroborate and 0.6 g ofbenzopinacol were dissolved together. 5 g of the dissolved admixturewere charged to a 4 dram vial along with 0.05 g of Ketjenblack. The vialwas placed in a J. Trembley Co. radio frequency heater, Model EO*1A andexposed to approximately 100 milliamps of radio frequency energy for 50seconds. A cured, hard, solid product resulted.

EXAMPLE 8

7.5 g of diglycidyl ether of bisphenol A, 2.5 g of trimethylolpropanetriacrylate, 0.3 g of diphenyliodonium tetrafluoroborate and 0.3 g ofbenzopinacol were dissolved in approximately 10 cc of methylenedichloride after which the methylene dichloride was removed by vacuum.The dissolved admixture was coated onto both cold-rolled steel and fiberreenforced, plastic adherends which were held together in a 1/2" lap toan adherend of the same composition with a binder clip. The thus clippedadherends were heated in a forced air oven at 160° C. for 20 minutes.After cooling to room temperature the adherends could not be pulledapart by hand.

EXAMPLE 9

7.5 g of diglycidyl ether of bisphenol A, 2.5 g of trimethylolpropanetriacrylate, 0.3 g of a BF₃ adduct, commercially available from Leepoxyunder the tradename "Leepoxy B-550", and 0.3 g of1,1-di(t-butylperoxy)-3,3,5 trimethylcyclohexane were dissolved inapproximately 10 cc of methylene dichloride after which the methylenedichloride was removed by vacuum. The dissolved admixture was coatedonto both cold-rolled steel and fiber reenforced, plastic adherendswhich were held together in a 1/2" to an adherend of the samecomposition with a binder clip. The thus clipped adherends were heatedin a forced air oven at 160° C. for 20 minutes. After cooling to roomtemperature the adherends could not be pulled apart.

EXAMPLE 10

The dissolved admixture from Example 8 was drawn down on a cold-rolledsteel substrate and also onto a glass fiber reenforced polyestersubstrate to form an approximately 5 mil thick coating. The thus coatedsubstrates were placed in a forced air oven to 160° C. for 20 minutes. Acured, tack-free, hard coating on each substrate resulted.

EXAMPLE 11

Example 10 was repeated with the admixture from Example 9. A cured,tack-free, hard coating on both substrates resulted.

EXAMPLE 12 Preparation of Ethylenically Unsaturated Prepolymer

900 g of toluene diisocyanate, 0.952 g of stannous octoate and 12.6 g oftriphenyl phosphite were charged to a 3-liter resin kettle equipped witha stirrer, thermometer and dropping funnel. 599.8 g of2-hydroxyethylacrylate were added dropwise over a 1-hour period whilemaintaining the temperature between 40°-50° C. by use of a cooling bath.The mixture was stirred for 2 hours at 45°-50° C. 0.952 g of stannousoctoate and 0.51 g of p-methoxyphenol were added to the mixture followedby the dropwise addition over a 11/2 hour-period of 1.056.7 g of abranched polyester of 1,3-butylene glycol, glycerin, adipic acid andphthalic acid sold under the tradename "LEXOREZ-5162-280" by INOLEX. TheLEXOREZ material contained 5.04 meq OH/g and had a hydroxylfunctionality of 2.6. The temperature was allowed to rise to 90° C. andmaintain thereat for approximately 2 hours at which time the NCO contentwas 0.02 meq/g as measured by IR. The resultant ethylenicallyunsaturated product was a clear glossy solid at room temperature. Theviscosity of the product at elevated temperatures ranged from 10,000 cpsat 71° C. to 14,500 cps at 90° C. The ethylenically unsaturatedprepolymer will hereinafter be referred to as prepolymer A.

EXAMPLE 13

5 parts of prepolymer A from Example 12, 5 parts of diglycidyl ether ofbisphenol A, commercially available from Dow under the tradename"DER-331", 0.3 parts of diphenyliodonium tretrafluoroborate, 0.3 partsof benzopinacol were dissolved together in about 20 cc methylenechloride and 3.5 parts of Standard-03 iron powder supplied by EMABondCo. were admixed therein. The solvent was removed by vacuum keeping theiron powder well mixed to form a thermoplastic adhesive. The adhesive ina one half inch lap, 20 mils thick tape was applied to one of twofiberglass and polyester composite adherends, commercially availablefrom Budd Co. as SMC substrates. The adherends were pressed together andcured for 60 seconds at 95-100% load on a 2 kw EMABond generator, ModelEA-20. The lap shear strength averaged 692±75 psi on five test samples.

EXAMPLE 14

5 parts of prepolymer A from Example 12, 5 parts of diglycidyl ether ofbisphenol A, commercially available from Dow under the tradename"DER-331", 0.15 parts of a BF₃ adduct, commercially available fromLeepoxy under the tradename "Leepoxy B-550", 0.15 parts of1,1-di(t-butyl peroxy)-3,3,5-trimethylcyclohexane were dissolvedtogether in about 20 cc methylene chloride and 3.5 parts of Standard-03iron powder supplied by EMABond Co. were admixed therein. The solventwas removed by vacuum keeping the iron powder well mixed to form athermoplastic adhesive. The adhesive in a one half inch lap, 20 milsthick tape was applied to one of two fiberglass and polyester compositeadherends, commercially available from Budd Co. as SMC substrates. Theadherends were pressed together and cured for 60 seconds at 95-100% loadon a 2 kw EMAbond generator, Model EA-20. The adhesive cured from aliquid to a hard solid. The lap shear strength of five test samplesaveraged 548±175 psi.

It is claimed:
 1. A heat curable composition comprising(a) a liquid,ethylenically unsaturated monomer, oligomer or prepolymer of theformula: ##STR13## wherein R is H or CH₃, R₁ is an organic moiety and nis at least 2, (b) an epox resin containing at least two ##STR14##groups, and (c) a thermal initiator member of the group consisting of(1)a substituted or unsubstituted diaryliodonium salt in combination with afree radical initiator, (2) a BF₃ adduct, (3) a BF₃ adduct incombination with a free radical initiator, and (4) dicyandiamide incombination with a free radical initiator.
 2. The cured composition ofclaim 1 as a sealant.
 3. The cured composition of claim 1 as a coating.4. The cured composition of claim 1 as an adhesive.